The manufacturers list decibal ratings for their condensers (outdoor units). Noise coming out from the ductwork vents is a whole different issue.

Our Carrier heat pump is now 10 years old. The outdoor unit was very quiet when first installed, but weather and age lead to rattles. I cut thin strips of rubber to act as bushings/washers to silence the rattles between metal/metal or plastic/metal connections (grill/body panels). Our Silencer system is now silent again.

We replaced the indoor air handler at the same time as the outdoor unit. I specifically wanted a quiet fan because our old one was loud. The A/C guy sold me on the single stage, variable speed unit and he also installed a sound deadening baffle where the air handler connects to the old metal duct work. In addition, the unit sits on rubber bushings on the concrete floor.

It works well, especially the way it slowly ramps up to speed, and is generally quiet. The only time it will make a loud noise is in the winter if you set your thermostat really low at night and then the metal ducts will pop in the early morning due to the higher thermostat setting coming on. We solved this problem by only dropping the temp 2 degrees at night for better sleeping/economy. Heat pumps tend to work best with small changes in demanded temperature. We also have the electric strip backup, but it rarely comes on.

It's been a great system, and I hope it lasts 20 years.

Great info thanks!

no matter how quiet the salesman tells you their heat pump is never install it near a main bedroom.